1. Field of the Invention
The present invention relates to a vibrational wave motor, a lens barrel and a camera.
2. Description of the Related Art
The vibrational wave motor is intended to generate a progressive vibrational wave (hereinafter, abbreviated to “progressive wave”) on a drive surface of an elastic body using expansion and contraction of a piezoelectric body, as publicly known from Japanese Examined Patent Application, Publication No. H1-17354, and so on. By this progressive wave, elliptic motion occurs on the drive surface, and a moving element in pressure-contact with a crest of a wave of the elliptic motion is driven. Such a vibrational wave motor is characterized in that it has a high torque even when the revolution rate is low. For this reason, the motor has the advantage that it is possible to omit the gears of a driving device in the case of the motor being mounted on the driving device, and to achieve silent operation with the gear's noises being eliminated as well as to improve the positioning accuracy.
On the other hand, the characteristics are unstable for this vibrational wave motor since it uses a vibration amplitude of about 1 μm generated at the stator. For the purpose of solving this problem, Japanese Unexamined Patent Application, Publication No. S61-35178 discloses making the amplitude at least 1.5 times the surface roughness of the drive surface to improve the drive efficiency and drive performance.